The press-leach system as above described is well adapted for the requirements of tanners, as its first cost is very small in addition to that of the construction of the leaches themselves; it extracts the bark well, and saves much labour in pumping, and greatly lessens the tendency of the pumper to miss pits in the series, to save time, when the master’s eye is not on him. Another advantage which is often important, is that when the leaches are full, much more than a single liquor can be run from the head-leach without pumping on; and similarly when they are run down to their lowest level, much more than a single liquor can be pumped on to the worst leach before it overflows. As the leaches flow slowly in comparison to the rate at which liquors can be pumped by a good steam pump, it is very advantageous to allow the pump to discharge into a liquor-tank raised to such a height that the liquor can be run from it into any leach at a suitable rate for the circulation, and it also enables liquors to be pumped without waiting till room has been found for them in the leaches. Similar tanks are very useful in running liquors for the yard, and especially for the suspenders in a sole-leather yard, enabling circulation to be kept up during the night, and at other times when the pumps are not running. They may also be used as filters for the suspender liquors by fitting them with false bottoms covered with a layer of nearly spent tan. The liquors may be distributed to the different pits and leaches by means of canvas hose-pipes, or, what is often more convenient, by overhead troughs, carefully levelled, and fitted with discharge valves where required. The latter are conveniently made of lead in a hemispherical form, resting on an indiarubber washer supported by a light brass casting, or a suitably turned rebate in a block of wood. (Cp. p. 457 and Fig. 79.) Such valves if good indiarubber is used, wear well, and are absolutely tight. [Illustration: FIG. 79.--Valve for Liquor-Troughs.]