outlaw
this is your shopping list at home depot and your supplier.
Tank,mounting hardware,float valve,in-line water filter,check valve for 3/4 I.D. hose,3/4 reinforced clear hose[how meny ever ft you need] ,hose clamps,3/4 inc spade bit with drill.
Mount your tank,take your drill and bit and drill a hole near the top of the tank[in the side] to install the float valve.[make sure you drill the hole far enuff down so the float will work and not hit the top of the tank].
Take the jumper line from your hose reel[garden hose reel] and cut it and install the in-line water filter[use the hose clamps].
Then attach the other end to the float valve.[you may need to cut off the end and push it on the float valve[use hose clamp].
Now install the bottom feed line[hose clamp]. Then install the check valve in that line about a foot from the tank.
Then hook the hose to your pump.[as a option you could also use another in line water filter,also double protection]
Fill tank and check that the float valve is working.
Disconnect the feed line from the pump and lay it down on the deck. Water should flow out. As soon as you have flow, reconnect to the pump.
Take the spark plug out of the wash unit. Pull trigger on gun and slowly crank the starter/pull rope to get the pump primed.
After all air is gone replace the plug and go to work to pay for all this stuff.
A 4 GPM wont need anymore then 3/4 inc supply line, your prob useing a 5/8 garden hose to supply it off the spigot anyways.
Keep your pump as low as you can, keep the pump as close as you can to the tank.
OPTION #1
If you DO NOT UPSTREAM you can take the return line off the unloader and route it back to the supply tank. You will need to drill a second hole in the tank and install a hose barb. Run a new langth of line from the unloader to the hose barb.
If you do this you can leave your pump in by-pass [let go of the trigger gun and lay it on the ground] for as long as you want and never hurt the pump or the unloader. This is highly reccomended.
TIM-this is why some run a tank even if you have a spigot handy.
Also while at home depot get the clamps that go 1/2 way around the 3/4 line and have feet on them[pipe clamps] and a box of drywall screws. This way you can attach everything to the wall/deck.
Hope this helps.
OPTION #2
On the supply line after the check valve comeing out of the bottom of the supply tank install a Y. One end to your washer and the other end to a 12 volt [on demand]WASH DOWN SHR-FLO PUMP.
WWW.GRAINGER.COM then from the washdown pump you can hook a reg garden hose up to it.
This way you can fill buckets,you can bleed down the supply tank[you dont allways want a full tank to travel around with] and if you have some help one day they can use it to rinse while you wash. You need a big tank to supply both at the same time but it is like having 2 wash units. This is very handy when i get help to wash trucks. It is also good back-up if you have soap on the surface and your unit breaks down. You can still rinse.