Thumbs up on the milk containers,,Only thing need is to rinse them well,best thing to do is to :
Rinse with hot water,
re-fill with tap water, add a lil bit of bleach,
fill to the top , put on cap,
shake and let sit for lil bit(10-20 mins)
pour out,rinse again,
fill with tap water, add a decent amount of De-chlor,
(Best De-chor to use is the kind with NO "slime coating" stuff for the fish in it,look around, most shops have at least one kind like that,vs, the
slime coat protection kind)
shake up the container, pour out,rinse in desired
make sure no chlorine smell is left in the container,,
Is use a lot of these containers for RO top off, Drinking water, Dog/bird water etc.
and DI, just mark the container ,if you use RO and DI,,i just mark the DI.
To fill these 1 gallons up , i use 5 gallon containers,the kind i get is from the "drinking water" area in the grocery store,,,sometime they have the 5g container,with handle and thread on cap on top,,
amd just pour the 5g into the 1g's,,,(the best funnel might take a few purchases to get the right one to sit in the 1g right,,)
One tip on the milk containers, after you fill them up , i like to put them somewhere i can watch them for "leaks" ,b4 i put them in storage spot. you will find that once inna while, one will get a pinhole leak somewhere,and leak out where you do not want it to,this way you catch the leaker b4 then,,,
Sorry for the long reply, just wanted to pass info along to you,,,from a long time user of these containers,,,