The 'rum fanny' would be taken by the mess 'rum bosun' to the place of issue. There, the number of 'tots' required for his mess would be measured from the 'grog tub' and poured into his 'fanny', the 'rum bosun' returning to the mess to distribute the tot to the mess members.
( A 'tot' being 1 1/2 gill of grog ).
The image left shows the rum issue in a messdeck.
The 'Rum Bosun', having just measured and drank his tot. The '1 1/2 Gallon' round fanny being used in this particular mess.
A large mess may require a '4 Gallon' rectangular fanny, all depends on the number of mess members.
Rum fannies may have been polished on the outside, but the inside would never have been cleaned.
One or more, '4 Gallon' fanny's containing water would be taken to the grog tub, the water used for mixing with the days allowance of rum, to make grog.
A little water may have been kept back to place into the tub after the grog issue was completed, to keep the timbers wet.
An even earlier variant exists in the photographic record, made of steel, shown in the image below left.
The image below right shows a round fanny made of steel, without a lid. I would guess from the same period.
Each of the two fannies below has a brass tally attached stating 'Royal Navy No XXXX Mess', where the mess name/number could be stamped into the tally.
( The image below left, is reproduced by kind permission of Mr David Bond - bonds-nautical-antiques.co.uk ).
Reinforced '4 Gallon', aluminium fanny. Base section of '4 Gallon' fanny, left.
Photographic records suggest that 'Fannies' of the type shown above, came into service in the early 1950's, exact date unknown to me.
Prior to the type shown above, the '4 Gallon' variant shown below, was in use, as far as I am aware, there is not a '1 1/2 Gallon' Fanny of similar construction.
The body of the Fanny is reinforced, as the handle bracket extends from one side of the pot, under the base to the other, it is riveted at several points.
The 'long side' of the Fanny' is reinforced also, forming a cross on the base, as can be seen in the image below right.
'4 Gallon' Rum Fanny. '1 1/2 Gallon' Rum Fanny.
The image above shows the '4 Gallon' and '1 1/2 Gallon' Mess Kettles.
The bodies and lids of both sizes are constructed from heavy gauge aluminium, the carrying handles are made of steel, as are the lid lifting handles of the '4 Gallon' fanny.
The official name for both items, given in the Admiralty Victualling Manual, is 'Mess Kettle', however the term 'fanny' is used with most recepticles.
Mess Kettles were used for a variety of tasks in the RN, the ones used for the rum issue being known to 'Jack' as 'Rum Fannies'.
'Four Gallon' rectangular and 'One and a Half Gallon' round, Royal Navy 'Mess Kettles' - ( Rum Fannies ).