A year ago I had to have my bus towed a few miles after its brand-new hydraulic fan motor split during its first test-drive (long story . . .). Good Sam sent a shiny new triple-axle heavy-duty wrecker with all the bells and whistles, and I do mean all the fun stuff! Hooking to the front axles wasn't difficult, but persuading the passenger-side axle shaft to release from its split cones under the eight nuts took many hard thwacks with a BFH until it came free. The driver said he always tried to remove axle shafts instead of disconnecting driveshafts, and for only a few miles tow he said it was OK to remove just one axle shaft - if he had towed it further he would have removed both. One other issue that I had planned for, but still was a slight problem, was airing up the bus to release the brakes: I had made an air inlet next to the door for connecting shop air or a tow truck's air to the bus's brake system, but it's for normal Industrial-style fittings, not the Automotive-style fittings the truck had. We had to jury-rig an adapter to get air into my bus, but I've now made a proper adapter for any future needs.
Yes, you can tow a bus with something smaller than a proper tow truck, but the risk increases, as does the level of interest that law enforcement may show when they see something unusual. A full-size pickup truck will move a bus on level ground, but don't even think about hills unless the bus's brakes are working. The brokers in Texas who buy school buses for export to Central America tow one behind another to the ports from where they are shipped. Many years ago when I worked for a moving and storage company in England one of our fully-loaded trucks broke down in Germany on its way back to England. It was a 2-axle DAF towing a 2-axle drawbar trailer, crammed full of several families' stuff and probably grossing about 30 tons. After much head-scratching the boss decided to drive out to Germany with his old Range Rover and tow it back. It took several days to drive from near Dusseldorf back to England, traveling at about 15 MPH the whole way back on small roads; the Dutch didn't want to even allow it through their border thinking it would break down even worse on their soil, but after a few bottles of Scotch had been donated to them they relented (we always kept a case of Scotch in our international trucks to help lubricate the wheels of commerce and bureaucracy, especially for trips behind the Iron Curtain). We had fun and games getting this whole mess off the ferry at Felixstowe - the bow ramp was too steep to get up, so we had to wait a few hours until the tide lifted the ferry enough to level the ramp, and then the British customs wanted to impound everything until they had inspected the entire load. (More Scotch also smoothed that situation.) Fun and games.
John