Originally I installed a 15 gallon plastic tank, a faucet, electric pump, and small stainless steel sink. I found I needed counter space more than I needed the almost useless little sink. Later I removed the sink, faucet, and pump and installed a gravity tap outside on the lower back of the trailer. This works much better IMO. Just put a bucket under the tap to collect the water when washing, etc.. Kick the bucket under the trailer when not in use.
The 15 gallon tank has been great during extended boondocking.
Q