If you need some type of plumbing supply, then this is the place. They are helpful about giving information over the phone, and in person (also, there are always plumbers there buying stuff, and they're pretty nice about answering questions). Sometimes you have to wait a while because there's no self service and you need someone to get your stuff for you. They have a lot of inventory, as evidenced by all the contractors that shop there. Felton Street is one way, so it's a little annoying to get there, but parking is not a problem.