LiquiVac for Trans Fluid Change

With the drain bolt removed the fluid comes out just like an engine oil drain. I'd recommend to take the plastic engine underpanel off; it might get splashed. The drain is pretty much complete, unlike a typical automatic transmission.

Fill is easy with a funnel with hose extension (about 3 foot extension). Keep the outside diameter to around 1/2" diameter max, so it'll fit in the fill hole. Just have the car level, and fill till it starts coming back out.

Note the Repair Manual excerpt (attached) says to remove the fill bolt first: good practice, just in case you have troubles. Also, it suggests to test drive and then recheck: I did that the first time only, and found no difference in level.

 

There is a drain plug and a refill plug you must unscrew/screw to change the fluid.
There is no dipstick.
So unless you are going to make modification to those, the vac won't work.
It's easy to do and doesn't take long.
It would partially work with the oil, but the dipstick tube doesn't go all the way down.

 

Are you talking about vacuuming the fluid out? There is no place to attach the hose too.
Some places use hose, either attached to the oil dip stick tube, or inserted through the tube
to suck the engine out.
But since the trans in the Prius doesn't have a dip stick, the vacuum cannot work.
You can use a tube snaked through the engine compartment to the refill hose on the tranny to
fill it up. That's how I did it, and many other also.
Or am I NOT understand your meaning???

 

But if it doesn't go into a dipstick tube, what would safely guide it to a low point inside? Too much potential for it to snag or jam on something important as you try to blindly guide it downward to a location low enough to slurp a significant amount of the fluid out.

Given that there is no official recommendation for changing the fluid, and even the most enthusiastic DIY might have the urge to change ATF about four times over the extended life of a lucky and beloved vehicle... I really think using the jack and drain plug is not a terrible forbearance.

If jacking up the rear of the car is too much of an extra step, skip it. What that changes is that the car isn't level for the procedure, so your drain will be less complete and your refill may be off by a bit. Measure what you drain and use that as a suggestion to modify the re-fill amount. Yes, you'd be taking a slight extra risk of error there but I think most DIYs could manage this successfully.

 

I believe the fill plug is screwed into a drilled and tapped boss on the upper surface of the transaxle case. Meaning, when you pour oil into it through a funnel the oil is almost immediately hitting an internal rotating assembly and then flowing around it until it finds level at the bottom of the void inside this casting. This is guesswork on my behalf, after having inspected my own car and studying some drawings of the transaxle.

In other words, it's not an oil tank. It's a box of gears and gubbins not entirely unlike the engine crankcase. Without a dipstick tube to mechanically guide the suction straw away from parts and towards the low point, it's going to be difficult, risky, and ineffective.