Okay here it is, today I procured 2 20 gallon aquariums for free with all the equipment and accessories to get them up and running. But I have a problem, they where severely neglected and need to be cleaned extremely well. (they set 1/2 empty for almost 4 years) with everything still in them. They are in bad shape and I really want to try and save both of them I will reseal if needed but from what I can tell the seals are fine. What I'm looking for is some real good ideas on how to clean them including the equipment (gravel under gravel filters, plants pumps heater)
I know the basic ways to clean and maintain tanks, but these are bad they even smell like dog pee?!
here is a couple pictures
Any help/suggestions will be greatly appreciated.

these pictures look better then the tank do in person

no that's not a crack at the bottom and the tank is empty

P.S. only if the pictures where scratch and sniff