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I have a 2002 2500 HD GMC Sierra Duramax for which I have purchased a RDS in-bed auxillary fuel tank. I need suggestions and/or instructions on a gravity feed installation. I have seen this type of installation on Ford and Dodge trucks, but GMC fill neck set up is different.

Ive Installed My Own Slip Tank On Several Trucks In Past This One That I Have Now Was Biggest Pain In Foot. Took Screws Out Of Filler Neck Behind Fuel Door & Removedgas Cap Pulled Fillerneck Down To Bottom Of Rockerpanel Drilled A Hole In Steel Part & Welded In A Steel (not Cast) Collar & Tied Hose From Tank To It W/ Filter. Have Seen Other Guys Actually Cut Rubber Hose In Half & Put A Piece Of 2" Pipe Between Hose This Also Works Good. There Is A Smaller (plastic) Hose Inside Of The Rubber One I Think It Is For Venting But Not Sure Either Way I Dont Think It Matters Though. I Also Used A 12 Volt Power Valve To Open & Close Tank While Driving(makes It Easier) Because It Will Throw Engine Codes @ You If Tank Dosent Stay Pressured Up

I drilled & tapped the fill neck for 1/8" pipe and screwed in a 90 degree hose fitting (5/16 ID hose on one end and 1/8" pipe on the other).

Not sure if gravity feed is legal. I used a small pump wired to an engine oil pressure switch (in case of accident pump is turned off when engine stops), with an on/off lighted rocker switch on the dash next to the air bag switch. I also added a return line from the fill neck back to the aux. tank--so fuel has some place to go if I forget to turn off pump when OEM tank is full.

Gravity feed on the fuel tanks is not legal.

Why not use the six way switching device from RDS?? I have installed and works perfectly every time.

Just at the dealer today factory rep. there looking over a gravity tank on a 2003 GMC C4500 it has been fixed under warrenty for last time the rep voided it as beeing not legal. The truck had a 300 gallion round side tank off a tractor-trailer the owner said he fill up at the house (home heating fuel) before going out on the road. What a Dope lucky he never whent to a inspection stop can see those chained braclets in use. Save up some more money and do it right the frist time.