tank draining
If we are not using the van for a while or it is this time of year I open both the emptying taps at the rear of the van whilst taking it to storage this gets rid of most of the remaining water bucause I go a particular route which includes steap inclines and sharp bends. Obviously I do not dispose of 'dirty grey water' on the road on down street drains.
My last van was from the swift stable, 2003 manufacture. The waste tank was under the van and an addition to the drain tap at the side of the van, the tank itself had a large opener on its underneath. Fresh water was inside under a seat and had a similar large opener on the top. If you open it, you might find a small plug on a chain inside enabling you to completely drain the fresh water tank. Just remember to put the plug back in! and on the waste tank, dont wear a long sleaved top, as it is bound to drop that smelly water straight onto your hand/wrist.
ps welcome to the site.
Jon