How this 39-year-old became a millionaire with an invention that potty-trains cats 

"Can I tell you something embarrassing that happened?"

Yes. Yes, you can.

Rebecca Rescate is sitting in the kitchen of her home in Yardley, Pennsylvania. The 39-year-old entrepreneur is getting ready to tell a funny story involving her annual gynecological exam.

But I'll get to that in a minute. (How's that for a tease?)

Rescate has created a lot of wealth and opportunity in her young life. She's launched several companies — she's the only person to appear on ABC's "Shark Tank" twice for two different products — but nothing has been as successful or as strange as her first idea: CitiKitty, a potty training kit for cats.

Why potty train a cat? "Kitty litter is gross," she says.

To date CitiKitty has sold 300,000 units with more than $8 million in total revenues, and Rescate feels there is plenty of upside left.

"You've got 8 million people who live in New York City, and probably half of them have a cat. None of these people want litter boxes."

"From the time I was 17, I realized I wanted to work with consumer goods," says Rescate. As a teenager she read "Why We Buy: The Science of Shopping," to understand how stores are designed to maximize sales based on human behavior.

Rescate graduated college with a degree in graphic design. Then she went to business school, but soon dropped out.

"There's a reason they recommend that you work before you go into an MBA program, so that you can actually know what they're teaching you," she says.

By 2004, Rescate was working in marketing at an enterprise software company, a job that did not excite her. She had recently married and she and her husband moved into a tiny New York apartment with her 11-year-old cat, Samantha.

"We got this 500 square foot apartment, and I decided to toilet train the cat." As one does... apparently.

Rescate searched for solutions online.

"There was, like, hundreds of people talking about toilet training on forums." Solutions included putting roasting pans under toilet seats and filling them with kitty litter to get cats used to the idea, so she tried something similar with Samantha.

It worked. "I was calling my friends, 'You have to get over here and see what she can do! She pees at 6 a.m., come on over!'"

Rescate had an entrepreneurial epiphany. "I always thought it would be fun to start a business, but I didn't have the right idea, and it wasn't until I toilet trained my cat that this idea fell in my lap," she says.

In late 2004 she went to work creating a product, seeding the startup with $10,000-$20,000 she'd received as wedding gifts. Her final prototype was a litter box that fits under the toilet seat with removable concentric circles to gradually train the cat to go straight into the water. Eventually the entire product can be removed.

"A cat's natural instinct is to cover the scent of its waste from predators," says Rescate. "Water covers the scent better than anything else."

With a prototype in hand, Rescate and a friend created the branding for CitiKitty and the training manual in one weekend. She found a manufacturer by calling around (she's still using the same manufacturer).

However, when she launched in June of 2005 and priced Citkitty at $29.99, some of her family and friends doubted anyone would buy such a weird product.

"Everybody laughed. They thought, you know, this isn't going to work," she recalls. "You're the last one laughing when it's selling and you're helping people."

First year revenues were $115,000, much better than the $40,000 Rescate was making at her regular job, so she quit. Revenues this year will come in between $700,000-$800,000.

CitiKitty is made in the USA, which impacts margins, but Rescate feels lower margins are more than made up for with quicker turnaround times and the lack of a language barrier. Local manufacturing turned out to be a big advantage when she went on "Shark Tank" and found herself completely unprepared for the jump in sales.

"I had, like, 400 units lined up," she says. "I think I sold 10,000 units from the airing, and I wasn't ready...thank God I manufacture in the US, right?"

As CitiKitty became a success, Rescate had to fight off copycats. She also looked for other products to launch, starting with a line of cat treats.

Then she hit a rut. "I was so caught up in the fact that I thought it had to be a cat product, and I couldn't think of another cat product." For six years, "I made nothing else."

Finally, she met someone seeking an investment as he launched his own product, the HoodiePillow, a pillow which includes a hood to cover your head. At first, Rescate merely wanted to provide advice, not an investment, but when she saw how successful the product was, "I changed my mind. I don't want to teach you to fish, I want to fish with you," she laughs.

She put in $100,000 and is now a co-owner of HoodiePillow. Since then, she's also created about a half dozen other products, from day planners to kids' blankets.

Oh yeah, back to the embarrassing story involving the gynecologist.

Rebecca Rescate was having her annual exam with a new doctor, and, well, he was busy doing his...job. If you are a female who has gone through this process, you know it's awkward at best.

Rescate blushes recounting the encounter: "He's trying to make small talk," she says. "He's like, 'What do you do for a living?' And I was, like, 'Well, I make consumer goods.'"

The doctor commented that her response was pretty vague, so Rescate told him exactly what she does. "One of my products...is a toilet training kit for cats."

She says the doctor stopped what he was doing, telling her, "You should have that product on 'Shark Tank.'"

She replied that she had already been on the show, at which point the doctor poked his head above the drape separating the top of her body from the exam area and exclaimed, "I recognize you!!"

It didn't end there. Rescate says when he moved up to do a breast exam, he wanted to know everything, bombarding her with questions such as, "Tell me what Kevin O'Leary is like."

And you thought making a potty training kit for cats was the weirdest part of this story.

Over the last 14 years, Rescate has had a lot of success, but she's also learned from her missteps.

One of the biggest mistakes she made as an entrepreneur was not trusting her gut. She always considered herself a strong person, "But for some reason, my natural instinct when a guy with a deeper voice — that's taller than me —would say something, I'd be, like, 'Oh, I should listen to him! He's got the stature for it!'"

It took her years to trust herself, and her advice to other women entrepreneurs with a crazy idea? "Never, never, never allow the sex of someone else dominate over what you already know."

More from Strange Success: How this dad's hairy back made him a millionaire

Like this story? Check out the Strange Success podcast.

Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank."