Been doing it for years. Bear in mind if you need to go upward a few feet it will create enough pressure to deform the top. Thats how we pump fuel to the dozer, tractors etc. I have 5 drums that have been retired due to deformation.
Here's a cheap way to do it. Buy a 2" to 3/4 PVC bushing. Procure a sharp knife and shave off the rim inside the bushing that prevents the 3/4 pipe from pushing all the way through the bushing. Cut the 3/4 PVC drop pipe 6" taller than a drum. Cut the end of the 3/4 drop pipe at a 25 to 30 degree angle. Glue the bushing into a PVC 2" threaded coupler. Drop the pipe in the drum angled cut down. Rub glue all over the pipe just above the threads on the drum, and then quickly shove the bushing over the pipe and THREAD into the drum before the glue sets. OR take your time and make sure you leave excess drop tube, and then trail and error the depth on it. That's my preferred method of doing it. it just tale about 10 minutes more. I have used water to lubricate the pipe going into the bushing and wet/dry pvc cement. It will be pretty hard to get the pipe to slide through the bushing even after shaving the rim away because it's tapered and designed to tighten on the pipe as it's pushed in. Once the drop tube is assembled buy a BRASS 3/4 to 1/8 bushing and then your typical scharader valve. REMOVE THE VALVE CORE from the schrader valve!!!
Ask me why you need to do this, or make a few messes first
...I use the little plastic dust cap when it's pumping slow or I need to walk away with pressure on the drum etc. Leaving the core in and trying to bleed the pressure off with a stick etc with the core installed IS NOT FAST ENOUGH once you need to stop the flow. Also if you use a 12V emergency type tire pump, it will allow it to work faster with the core removed.
Buy brass so it'll be easier to remove as needed, galvanized or black steel can be a pain once it's been rained on a while.
A 7 GAL rescue air tank filled to 125 PSI will hold exactly enough air to empty a drum a few feet (2-4 ft) uphill using Diesel.
Diesel pumps pretty quickly that way, the dozer holds 80 gals, and we can empty a drum in about 8 to 10 minutes.
Oil at 100 percent is fairly slow, and gets irritating waiting on it to fill my 19 gal tanks on the truck, but thats still how I do it.
If you deform your drum, you can only beat it back out a few times before it either starts leaking, or you can't get the last few drops out due to the drop pipe no longer touching the bottom. Raise the pipe an inch off the bottom or more to your liking, it will speed the flow up very slightly.
Words of caution.
Rain collects on a drum top. The rim of a drum is taller than the rim on the fittings. If your fittings are not AIR TIGHT, they are not water tight either, and it WILL get in. Ask me how I know,,,,John Deere fuel filters get expensive.
PVC will hold up fine against gasoline, and diesel, as well as oil, but NOT SUNLIGHT! paint the fittings etc.
When a drum is half empty, spring and fall temperature changes can cause enough pressure to build and spill 10 to 20 gals of oil/diesel on the ground etc. Ask me how I know, install a cap or valve on the exhaust line. The material used in PVC valve seals can get "sticky" after use with fuel, and make it very hard to turn the valve on and off, so I don't use them, except for o my super sucker. I just slip a cap over the end of my pvc pipe. I have a 1" rubber line connected to the drop tube on my drums, and the another 3/4 piece of PVC on the other end with a 90 or 45 to make it easier to fit into the filler necks of my stuff, thats where I slip the cap on, and use a bungee to hold it on.
A 12V emergency tire pump will empty a drum, but it takes a lot longer than I'm prepared to wait sometimes.
A 1 Gal sprayer with the hose adapted to the inlet side of the drum is much faster and obviously more reliable in the event of no power.
Words of warning
It only takes around 30PSI, so I have read to blow the lid off a metal drum, and 40 or so for plastic. Perhaps for the sake of prosperity, I'll blow one of my old ones up just to see!
If you leave the valve core in the valve, and need to stop the flow quickly for whatever reason, you will not bleed the air off quickly enough with the core in. The less liquid in the drum, the more pressure it takes to start the flow moving, and the longer it takes to bleed enough pressure off to stop the flow. You have to plan ahead when doing it the poor mans way. The lower the level of liquid in the drum the more forethought that needs to go into how much pressure, and when to start bleeding it back off. On the drum I use at home i leave the 1/8 fitting removed, and use a air wand to pressurize the drum, and it allows the pressure to bleed back off when needed in 5 or 6 seconds.
