E8 dissections

Sacrifice mothers 1 at a time with CO2
Wet belly with EtOH to prevent hair from getting everywhere
Cut open and remove uterus with implanted embryos. Keep in cold PBS on ice
Open sacs 1 at a time to remove embryo
First remove outer membrane and extraneous fats (muscular uterine lining)
Then transfer to clean PBS to open up fluffy stuff (decidua). Open from the sharp end. Embryo is in the sac in the hole.
Transfer sac to clean PBS to minimize maternal tissue contamination
Remove trophectoderm
Cut off amnion and keep in labeled eppie in a drop of PBS (the drop that carries the amnion on the forceps)
Put embryo in 4% PFA/PBS for 1h to fix (24 well plate)
Transfer to PBS at 4C
Store until further use

For reference, read
Dissection of 6.5 dpc Mouse Embryos