To put Toffee to sleep???

Question
Hi Sandra,
hope your well? Well it's not great news. My poor little baby has grown really old over the last few weeks. She has nearly made it to her third birthday. She has got a tumour under her front leg, possibly a tumour by her back end, large cataracts in my eyes, she is deaf and can't hear me and she has got advanced HLD. I took her to the vet this week. I've told him she is still eating and still wants to interact with me so because of that was reluctant to PTS... The tears are flowing now.. He agreed with me but said she probably hasn't got much longer and didn't recommend operating on her tumours.
The vet was on Tuesday. Today I've noticed that she is dribbling a bit round her mouth. Usually when I scratch her back end she starts licking me, but today she bit me. Usually when I give her smoothie on the end of my finger she licks it but again she bit me.
I'm so sad as I think she has had enough but I don't want to remember her in her last few weeks as a biter. She has never bitten me in her little life.
I don't know what to do. In my heart I think it's going to be a final trip to the vet.
What's the best way to ask for an animal to be put to sleep? I mentioned it to my vet and he said he puts an injectable sedative into her rear end and I can hold her while she goes. He then injects the final lethal injection. Is this ok? I don't want her to suffer. He said he doesn't use a sedative chamber as doesn't like them.

Thanks
vicky

Answer
Oh Vicky :(

I feel like I know Toffee....I have heard about her for a few years now, watching her grow and change, watching and waiting anxioiusly while she has mammary tumors removed....and now.....this.
:(

I am so sorry it is coming down to  this  decision.    
I need to ask if the vet plans on injecting her heart....you must ask this.  PLEASE DONT LET HIM DO THAT IF SHE IS NOT OUT, totally under anesthesia, not just sedated.

I am so sad about this......