I promised to supply chapter and verse on this drain-a-lotta-gas
stuff.

The document is called:

Airplane Flight Manual
Model PA-28-235
Serial Number Effectivity: 28-10001 thru 28-7210023

The approval info says:
FAA Approved 7/1/63
REVISED 9/1/71 Rev. No. 19

I do not know if there are futher revisions that extend the
applicability.

A note on the cover says:
THIS DOCUMENT MUST BE KEPT IN AIRPLANE AT ALL TIMES
REPORT VB-170

Here's what it says:
(limitations, placards and autopilot stuff deleted)

10. Fuel System Pre-Flight Procedure

The fuel system should be drained daily prior to first flight and
after refueling to avoid the accumulation of water or sedient. Each
fuel tank is equipped with an individual quick drain located at the
lower inboard rear corner of the tank. The fuel strainer and quick
drain valve are located in the fuselage at the lowest pointof the fuel
system. It is important that the fuel system be drained in the
following manner:

a. Drain each tank through the individual quick drain located at the
inboard rear corner of the tank making sure that enough fuel has been
drained to insure that all water and sediment is removed.

b. Place a container under the fuel sump drain outlet, which is
locted under the fuselage.

c. Drain the fuel strainer by pressing down on ghe lever located on
the right-hand side of the cabin below the forward edge of the rear
seat. The fuel selector must be positioned in the following sequence:
off position, left tip, left main, right main, and right tip while
draining the strainer to insure that the fuel lines between each tank
outlet and fuel strainer are drained as well as the strainer. When
the fuel tanks are full, it will take approximately 11 seconds to
drain all the fuel in one of the lines between a tip tank and the fuel
strainer and approximately six seconds to drain all the fuel in one of
the lines from a main tank to the fuel strainer. When the fuel tanks
are less than full, it will take a few seconds longer.

d. Examine the contents of the container placed under the fuel sump
drain outlet for water and sediment and dispose of the contents.

(performance data snipped)


Don