Most shops have compressed air and I use a double diaphragm pump I scored off Craigslist moons ago. They are able to pass some particles and pump thick stuff. Colder months it freezes up but I just poor hot water on it if I am outside. But it never get tired. I carry both style of air connectors. I put some mesh over the pick up tube so it keeps the big stuff out. Amazon or ebay have them for cheap now. If you do suck something up that jams up one of the check balls they are easy to disassemble and clean out. If the shop doesn't have air then I bring my gas compressor. Also put a ball valve on the airline and have two airlines. This is so you can control the speed of the pump and cut the air when it is time to switch containers. This setup allows you to stand next to the container while filling and watch it. They do gravity syphon if you filling a small container lower then your source.
For transporting. Barrels are the best for being inconspicuous. I used to swap out barrels and role them up on ramps into a trailer or pickup. But that is heavy. They are relatively easy to handle full after some practice. Also easy to pump into and suck out of. I like totes now but still use barrels. If they have a forklift then its easy to load with the forks. Or swap totes out. I like to pump cause then its already presettled if you don't suck off the bottom.
Others have said this before. Some rules to think of as part of the "oil club"
-no spills. Be clean, if you show up like a hobo and leave a mess it leaves a bad impression on all of us.
-no spills
-never walk away while you are pumping. if something is going bad you are there to catch it before it gets really bad. That being said have a fast enough pump so that your not temped to walk away. If you have to walk away always shut things down so they can't go bad.
-Have stuff to clean up a mess. Spill kit
-be respectful and professional. They are giving you oil for free a lot of the time. Most of the time they are more then happy to work with you and really accommodating.
-bring thank you treats; donuts/pizza/tacos. Not going to break the bank sense you are saving money using their oil. I would show up around lunch time at one friend's shop and hang out when I would bring food.
Hopefully this is helpful and welcome, cheers