I used to drive milk reload (trunking in artics) at 38 tonnes years back and then a few years later at 44 tonnes - maybe I’m a smooth driver but I found it actually doesn’t slosh anywhere near as much as it used to. The tanks are still around the same size - 30000 litres or so, if you have 28-29000 litres on your notes then by all means have some respect for the load but don’t expect it to move much as the tank is near capacity and there isn’t much room for it to move. In the old days at 24000 ish litres though - look out! Don’t know about baffles, you don’t necessarily know when you have them now as often there is no access to tank top to look in (elfin safety) but in the old days you’d get quite a few twin-pot milk tanks which IIRC where worse when braking than single potters. If farm collection work it varies how full you are through the day (obviously
) so they can still swill about lots - and it is genuinely surprising how violent it can be until you get used to it!
Good advice above from Toby on venting tanks ^ ! I’ll add that with venting:
- make sure you know what you’re doing, if in doubt it used to be pretty foolproof to open a top hatch and leave it sitting on a latch (open an inch or so) but with h&s lots of tanks now have no access ladders and often no top hatch (and no don’t open the one on the side!!!).
-Tanks usually now have air valves for vents and CIP (washing) lines but after five+ years some of the labelling wears off so don’t just guess - better to ask someone.
-And close vents before leaving the yard with a full tank too, as milk ■■■■■■■ out over the road doesn’t go down well with plod.
-On some tanks there are taps on the cip pipework coming down from the top of the tank which need closing to travel/opening to unload/wash: tap handles in line with the pipe means open, at right angle is closed.
Washing as very important as someone above mentioned - always check the wash book before you leave with a full trailer (the book is kept with the trailer, usually in a plastic tube in the outlet locker or in a metal box by the sideguard) and if it hasn’t been washed in the last twenty four hours make sure someone in charge knows about it before you leave! Similarly always make sure you fill in the book when you wash the trailer.
Last tip from me - if samples are required from a dedicated sample tap always run a bit out before taking the sample (in case there’s dirty old stuff in the sample line which could get the load refused), and during the wash cycle leave the sample tap open so it gets a run through of all the wash process.
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Oh and if you’re talking reload/trunking not farm collection, then never assume it’s just a day job, if a processing site goes on stop for unforseen reasons they need to get the product pasteurised within so many hours from the farm so it’s either a case of getting checked in and WAITING (this can mean 24 hours plus) or being diverted to somewhere else (possibly bloody miles away) where they CAN take the product, possibly en masse with a bunch of other untipped artic loads. Westbury Dairies is a prime example of this kind of debacle, great when the going’s good, AWFUL when it’s not. 
In general though, the milk trunking is good, clean, easy work. Go for it! Milk farm collection, same applies, but not so clean 