Liz Lerch loves cats, but not having to clean their mess out of a litter box, or spending hundreds of dollars on litter over the life of a cat.

So when she got two 4-month-old kittens from a shelter, she vowed to train them to use the toilet in her Lombard home.

Following advice from the book, “How to Toilet Train Your Cat,’’ Lerch put cardboard over the toilet, then a plastic planter holder with a hole in the middle of the bottom, filled with litter. She gradually removed the litter and widened the hole, until there was no litter and the hole was as big as the bowl.

Each time cats Carl and Stewie used the potty, she gave them positive reinforcement — praise, petting, play or food.

There were mishaps of course, but those were blamed on an unfortunate bout of irritable bowel syndrome.

After nine months of practice, the cats now use the toilet on their own and seem perfectly happy. And, yes, humans use that toilet too.

Some visitors, like a guy who worked on Lerch’s garage door, are a little freaked out by her cats’ routine, but most of her friends had a positive reaction.

“My friends all want to see it happen,’’ she said. “They think it’s cool, and want to know why nobody toilet trained their cats.’’

Not a new idea

Toilet training cats is not new. Jazz musician Charles Mingus wrote publicly about training his cat decades ago. The practice got more recent boosts from a toilet-trained Jinx in the movie “Meet the Parents’’ and coverage at online sites like Craigslist or karawynn.net.

Cat owners can buy kits from outfits like CitiKitty.com, which sells toilet-training covers for cats. Some owners even train their cats to flush by putting a toy on the handle.

Lerch’s cats get wet sometimes splashing the water with their paws, but they’ve never fallen in.

Still, not everyone is jumping on the toilet-training bandwagon. Some people don’t want to share a toilet with a cat or find their unflushed presents.

What about instincts?

Others, like Betsy Lipscomb, who sells cat supplies and writes the online advice site Cats International, say cats need litter to meet their instincts to dig and cover their waste. She cited cat owners who’ve tried toilet training and ended up with soiled carpets.

“Some people want to make their pets into little people with furry coats,’’ she said. “It’s going to backfire when you can’t satisfy the cat’s natural instincts.’’

Before Liz Lerch had success with Carl and Stewie, she learned through experience that some cats just won’t go without litter.

She previously tried potty-training her cat Springsteen, but when she tried to take out the litter, he drew a line in the clay sand.

“He would meow and walk up and down and look at it and act like he had to go,’’ Lerch said. “He’d look at you like, ‘I gotta go but there’s nowhere to go and you took my stuff.’”

She kept flushable litter in the box, but eventually that became more hassle than it was worth to clean.

“When you step out of the shower and into cat litter all over the floor, it’s not the most pleasant thing,’’ she said.

Ultimately, she gave in and let her cat return to the traditional litter box, figuring he was set in his ways at age 10.

American Humane Association training manager Karen Spaulding said her group has no stance on the issue, encouraging what works for both owner and kitty.

“I had a friend that did it beautifully and never had a problem,’’ she said, “but you might need the right cat and the right situation.’’