I think you might be new to these 240s.
Anyway, coolant flushing is a bit different from what you might expect.

Heater hoses are nearly inaccessible, located in the firewall near the tranny and engine oil dipsticks. So you can forget about a "T" fitting there for a traditional forced flush.

I think most folks just yank off the lower radiator hose and let the stuff spill. You can see that lots stays in the block that way.

Radiator has no petcock (maybe some aftermarket ones do). However there's a drain petcock on passenger side of block, about as low down as the oil filter is, but near the rear. At 3rd of 4th cylinder. It's brass. You can turn the outer smaller hex with a wrench. Likely it will come out before any fluid flows as they are usually clogged, then you clean it out. I like to use a bit of soft pvc tubing (5/16 or probably 3/8" i.d.) on the nipple to carry fluid to a container. Inner larger hex attaches it to the block. Fluid will flow very slowly if reservoir cap is on tight, flows better with cap off.

I avoid yanking on the radiator hoses especially where they connect to the rad. Radiator necks are plastic. They last for decades but a cracked neck is often what kills off these radiators. So that's why I drain at the block petcock rather than pull off a hose.

So -
Heater valve open.
Engine cold or run just a minute or two, not hot.
Prepare a water source to replenish water as you drain it (garden hose if not frozen).
Drain fluid from petcock and close petcock.
- Remember it's brass, don't overtighten.
Remove thermostat and its ring gasket.
Replace t'stat housing medium-snug without t'stat.
- It will not have a really good seal but this is temporary for flushing only.
Fill system with water.
Start engine and let it idle.
Remove reservoir cap.
Reopen petcock for a moderate flow.
Top off fluid from garden hose as reservoir level goes down.
Do this till fluid flows clear then a couple minutes extra for good measure.
Drain water, add 5 qts anti freeze, then top off with distilled water.
Replace thermostat and gasket.
Idle till t'stat opens, then top it off and button it up.

Even when fully "drained" there's still a good quart or two in bottom of block due to the hose layout. That's why I add 1/2 the system capacity of antifreeze (5 qt) when it's as empty as I can get it. Then add water to top it off. If you premix the antifreeze you'll never get it all in, as you're starting with a couple qt plain water in there already.
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Sven: '89 245 NA, 951 ECU, expanded air dam, forward belly pan reaches oem belly pan, airbox heater upgraded, E-fan, 205/65-15 at 50 psi, IPD sways, no a/c-p/s belt, E-Codes, amber front corner reflectors, aero front face, quad horns, tach, small clock.