Receive one large (60 x 80cm)delivered to your door on a subscription plan of your choosing for a flat rate per unit. When the new grass arrives simply put it in the large box where you want your pet to toilet & the old grass straight into the bin. The grass can go into general or green waste and the carton into the recycling, simple as that! Most pets don't need training, they instinctively want to use it.
The grass will absorb the urine through the root systems as if it were water, you still need to collect the poo (bugger I know!).