Follow along for a flush bottle build that is cheap and easy to build plus it also provides some added safety by utilizing a check valve to eliminate flammable fume discharges and helps to prevent dangerous spills if the bottle tips over while in use.
First step is to get together the need parts which are fairly common items and most have easy access to plus one of parts can be purchased off of Ebay for as little as a couple bucks.
Ok. lets get started, first item you need is a large mouth plastic bottle like many motor oil bottles of today utilize, other items are 4ft. of fuel line, a inline fuel filter, 2 - 5/16th bolts, 4 - 5/16th nuts, and a inline fuel check valve which can be bought off of Ebay.

Notice the large mouth opening on the bottle. The large mouth is needed so that you can drill and fit 2 bunges through the bottle cap.

Take the 5/16th bolts and cut them off to form bunges which will be bolted through the top of the bottle cap.

Once you have the bolts cut it is time to drill a hole thru the center of the bolt for both fuel and air to pass through. Drilling is best done on a lathe but can also be accomplished in a drill press but with great care.

Once you get the bunges done, drill 2, 5/16 inch holes in the bottle cap and install the bunges in the cap. You are now ready to hook up the related fuel and air lines.
Pick any of one of the bunges coming through the cap and install your check valve with a piece of plastic fuel line so that the bottle is able to draw air but won't allow fuel to run out if the bottle is tipped over. Note the direction of the arrow, this is the direction the valve opens in.

On the remaining bunge put a piece of fuel line down below the cap that is about 2 inches short of touching the bottle bottom when the cap is installed and slide your inline fuel filter into the fuel supply line near the bottle bottom so that you are assured that you flush will be filtered before it goes to your engine.

Take a piece of fuel line at least 3 ft long and install it top side of the filtered bunge, this will be your engine feed line and 3ft should give you plenty of working room when you are flushing.

When not in use slip the carb feed line over the check valve intake top and you have a completely sealed system for transport. When needed for flushing simply pull the hose off the top of the check valve and slip it on to your carb fuel inlet.

There you have it, a safe effective system for flushing out your favorite American racing engine.
R.E.A.R.