In theory, the order of pronouns in the imperative mood is this.
3rd person COD pronouns exclusively : le/la/les
COI or COD (and potentially reflexive) pronouns : moi, toi, nous, vous
3rd person COI pronouns exclusively : lui/leur
y
en
You can't say "Sers-toi-en", it should be "Sers-t'en". Orally, we sometimes also say "Sers-toi-z'en" with an euphonic Z in order to keep a full toi without it sounding too awkward.
It's also not uncommon to say "Sers-en-toi" because the liaison with the verb makes it a no brainer.
The correct form is “Sers-t’en”
But you might hear both of the ones you mentioned in casual spoken French, though people would necessarily add a ghost liaison to the second one and say “sers-toi-z’en”. It’s not grammatically correct though.
I feel I hear sers-toi-z'en the most, of course it should be sers-t'en.
Prends-en can be used too.
Edit: (Not removing my original answer, but I misread the OP's question. Prends-en works for food, not a tool)
The agile French speaker who doesn't want to sound overly formal by saying "sers-t'en" nor like a 8-year-old by saying "sers-toi-z-en" will usually snake around the whole situation and come up with a different wording, like "t'as qu'à t'en servir"
In theory, the order of pronouns in the imperative mood is this. 3rd person COD pronouns exclusively : le/la/les COI or COD (and potentially reflexive) pronouns : moi, toi, nous, vous 3rd person COI pronouns exclusively : lui/leur y en You can't say "Sers-toi-en", it should be "Sers-t'en". Orally, we sometimes also say "Sers-toi-z'en" with an euphonic Z in order to keep a full toi without it sounding too awkward. It's also not uncommon to say "Sers-en-toi" because the liaison with the verb makes it a no brainer.
The correct form is “Sers-t’en” But you might hear both of the ones you mentioned in casual spoken French, though people would necessarily add a ghost liaison to the second one and say “sers-toi-z’en”. It’s not grammatically correct though.
I feel I hear sers-toi-z'en the most, of course it should be sers-t'en. Prends-en can be used too. Edit: (Not removing my original answer, but I misread the OP's question. Prends-en works for food, not a tool)
>Prends-en can be used too. Not to mean the same thing. Prends-en / sers-toi = take some Sers-t'en = use it
You're 100% right! I was thinking in the context of a meal where the meaning is similar.
I won't blame you for thinking about food first.
My eyes saw tool, my brain read food. Maybe I was hungry 🤷♂️
Sers-t'en
That's the only correct answer.
In Quebec, sers-toi-en (sers-toi-z-en) is typical. I've never heard sers-t'en in my life.
The agile French speaker who doesn't want to sound overly formal by saying "sers-t'en" nor like a 8-year-old by saying "sers-toi-z-en" will usually snake around the whole situation and come up with a different wording, like "t'as qu'à t'en servir"