Jacob O’Dell, 24, was serving a three-and-a-half-year sentence at HMP Peterborough when he launched the vile attack in December last year.
O’Dell armed himself with the bucket, which contained a mixture of urine and faeces, and hurled its content towards the guard.
The attack, which is commonly referred to as “potting”, left the victim covered in faeces, despite her attempts to shield herself.
When interviewed, O’Dell claimed he was pressured into committing the offence by another inmate.
He later admitted charges of administering a noxious substance with intent to injure.
O’Dell was jailed for an additional 18 months on Monday (2 November) at Cambridge Crown Court.
DC Zoe Slater, from Cambridgeshire Constabulary, said:
“This was a disgusting, unprovoked attack that nobody should have to endure.
“Prison staff work hard to ensure the safety of inmates and should be able to do so without fear of being attacked.”