Idea... any chance you could put a piece of St. Augustine grass instead of the plastic grass and just replace that ??? Is there enough space to put water at the bottom for the pee & the water? Kindda a hydroponic type thing??? Just a thought! ??

what is st. Augustine grass? not sure what you mean with the water. In the pan under the grass?

St Augustine is the grass in our front lawn in Texas, it's very hardy for dogs.

The thought was to put real grass (instead of fake grass) in a pan of dirt/water. Seems that it would be easier to keep clean and wash out? Just a thought.

I have been intrigued by the idea of the soil-free Marathon Lite sod sold by dog. com for pups and small dogs. It seems to grow in a hydroponic mat.
http://www.dog.com/item/pet-a-potty-marathon-lite-sod/102231/
The one time I wanted to use it, they were out of it.
I think that you could order several, and the pups would be trained to real grass. No soil, so no dirt, no worries of heavy metals, unless there is more to hydroponic style grass than I know. I would tend to want to rinse it and let it dry before first use.