Potty Pads
There are disposables and then there are Lenny Pads. Originally salvaged from nursing homes but now made to order for dogs, they are still very reasonable and last for hundreds of washings. After hosing them off, just drop them in your washer. I start all my puppies on these cotton pads that are waterproof on one side and very absorbent on the other.
Websites that I use frequently include: