Soap Tanks Are More Work
Pressure washers provide the best results when you pretreat with pressure washer soap. Some machines include an onboard soap tank. We initially thought that was a great idea. But we found it to be a nuisance overall. We had to constantly refill the tank on large jobs. And afterward, the tank needed to be cleaned out (dried soap can damage the pump).
Instead, we prefer the siphon tube approach. Just shove the end of the tube into a gallon of cleaner and start soaping. When you're done, rinse the siphon tube, cap the jug and call it done. You can convert a machine with an onboard tank by disconnecting the tank tube and installing a siphon tube/filter accessory to the soap port on the pump.