We can’t solve player ethics.
We can only help treat the symptoms.
Clearly state that you need mana in chat and then sit and drink tell you are over 80%, if they rush forward and pull and die that’s on them, they will learn really really quick to wait for mana or too take less damage so you don’t need to burn so much.
or they kick you and you apply for a new key and get through 4 other keys before the bad dps get a single invite or the bad tank find a healer over geared enough to carry them.
here the thing. Not sure what tanks you are meeting but tbh other high dmg phase you really shouldnt be spamming the tank that much.
My healer generally dps and only really start spamming me when I yell help. Saying that tbh you’ll be fine to sit down and drink while they pull small . I do that alot w/ my group. Don’t have the feel that you need to spam heal on the tank always. They have defensive they can use in the mean time. Unless of course the tank is just useless and dont know how to use his cooldowns
Seriously? Nobody’s trying to torture the guy by running him out of mana. Nothing about this is unethical.
then you’re clueless. I’m willing to bet you’ve never done a single m+. What we’re doing here is giving him advise to how to optimized how he regain mana back while trying to not slow down the run.
Well people enjoy the game differently…some like to go fast, some like to take it slow. And, people normally don’t care about strangers, so don’t expect pugs to be nice. It won’t happen…most of the time.
You drink between pulls. Most tanks will stay alive while you get like 25% mana. Those who cant deserve to die.
The worst is borked pulls into pride when you have no mana
Also use mana pots to take the edge off and use CDs wisely. Knowing when dmg is incoming helps sneakin drinks
Saying that you’re OOM, sitting to drink, and having the tank wander off while you finish to start the next pull isn’t a new thing at all. It’s pretty commonplace and it’s not particularly fun if the group is just standing idle staring at walls waiting for the healer to drink to full each time. It’s not something that’s necessary and if one is on a timer, the group can’t stand around doing that anyways.
If mana is a concern going in then the healer needs to have a quick convo with the tank: what pulls may be the hardest, to please keep half an eye on their mana bar and the like. It’s a conversation I’ve had with tanks when I’m healing, and as a tank, have had healers talk to me about.
If the group can’t be bothered to wait for a healer to get mana [and worse, stands in all the bad stuff] that’s on them, no matter what they rage in chat. And part of this issue for the OP may be using expensive heals when smaller heals would be fine. That kind of a thing comes with time, understanding the tank classes, and in the end, will also help conserve mana usage just like higher gear and group coordination.
As a tank, I keep my healer on focus in dungeons and check mana every so often. In raids, it’s my co-tank who gets the focus.
I find that really helps identify when to coast versus when to continue.
Voice coms it’s usually much more up front and consistent communication.
managing cooldowns is a great way to conserve mana in m+
if you’re having trouble because the group is bad though, you’re going to have to improvise and figure it out though (which many of us PUG healers have learned to deal with) 
Tyrannical weeks and grievous weeks will always be hard on mana though, so bring pop! 
Use shadowfiend more
Buy foods, make foods or mage foods.
To give the benefit of the doubt, as tank im constantly asking heals if they’re good. I get a response 20% of the time.
Saw a heals at 10% mana. Asked them 3 times and they said they were good. At 3rd boss their mana pool reset to 90% at nearly times. They claimed it was like that the whole time.
So maybe tanks just assume heals will say if they need mana. In my experience I have rarely had a tank ignore me. It still happens, maybe bcz they’re used to blazing thru. But it seems like a complicated issue
You don’t need to jump in the fight immediately finish drinking, if you need to and the tank can’t survive until you get mana than that’s severely a tank fault and nothing you can do other than ask, or play with better people.
But with pride it’s hard to ever drink so maybe your doing too low keys? I’m 6/8 to ksm and tanked 4 of them I think and plenty of 13-14s and the healers never drink it my keys
I run with my guildies, so my tanks and I have a synergy when it comes to me drinking and them pulling. I’m really lucky. 
As a disc priest main I feel this in my heart. However I have found a group that has been working a lot better than what I used to have. Pugging can be too stressful to try but I’d say find a group to run with and it can be infinitely better. Especially if they are willing to hear you out and listen.
Also, spiritual clarity pots should be kept. They aren’t everything but they do make a difference for sure.