Step 1: Gather tools and materials
a PVC pipe cutter, hacksaw, or some other way to cut through PVC pipe
a power drill
a 3/32" drill bit (just a tiny bit larger than the needle of a ball pump)
a file or knife to clean the ends of the PVC pipes
materials from the hardware store:
about 3' of 1/2" schedule 40 PVC
about 2' of 1" schedule 40 PVC
1 1" PVC ball valve
1 1" PVC cap
1 1" --> 1/2" threaded PVC reducer bushing
1 1/2" --> 1/2" threaded adapter
materials from the dollar store:
1 ball pump
4 zip ties
Step 2: Cut the PVC pipe to length
Use your saw or PVC pipe cutter to cut to the appropriate length, then use a file or blade to clean up the area of the cut so it will fit in to the fittings.
Step 3: Dry fitting
From front to back the order of the parts will be:
barrel of 1/2" pipe (will be glued to the...)
1/2" --> 1/2" threaded adapter (will screw into the...)
1" --> 1/2" threaded bushing (will be glued to the...)
ball valve (will be glued to the...)
compression chamber of 1" pipe (will be glued to the...)
Step 4: Glue!
To glue PVC, clean the area to be cemented then swab both parts with a dab of purple PVC primer. This sets almost instantly, allowing you to apply the cement. PVC cement is nasty stuff - use ventilation and don't get any on your skin. Like hair gel, a dab'll do ya. Once the cement is applied, fit the parts together tightly. Use a paper towel to wipe up any excess. Allow five minutes to dry.
Step 5: Drill
Plan your angle carefully, though - you don't want the needle bending when you rest the musket, but you also don't want the needle to miss the pipe.
Step 6: Prepare the needle
Step 7: Attach the pump
Attach the pump itself to the compression chamber using the zip ties. You will probably need to attach two ties to each other to get all the way around. Once it is on tight, clip the excess and you're done.
Step 8: Operation
If you are using something that won't easily slide down the tube, the threaded connection between the barrel and the ball valve can be undone and ammo placed in the barrel from that end.
If muzzle loading, be sure the valve is in the close position when dropping in ammo.
Close the valve and compress the pump about five times. Aim and release the valve to fire.