All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
If it is possible to wash and rub the corpse which you mentioned without causing its decomposition or rupture, then it must be washed with water and rubbed, but if the corpse is harmed by doing so, to an extent that it breaks apart, then one should only pour water on it. If it is not possible to pour water on it because of fearing that it will break apart, then one should wash whatever part of the corpse that is possible to wash, and then perform Tayammum (dry ablution) on the rest of the corpse. Ibn Qudaamah said: 'If it is possible to wash the drowned, burnt corpse and the one who died because of smallpox, then one should wash them, but if it is feared that they will decompose because of the use of water, then they should not be washed with water, rather dry ablution is enough if possible, this is like the live person who is harmed by water. If it is not possible to wash the dead because of the lack of water, then Tayammum should be performed on him, and if it is only possible to wash some of his limbs, then what can be washed, should be washed, and Tayammum should be performed on the rest of the corpse.'
Allaah Knows best.