More than 2,000 people, from church and community groups in the capital, arrived in the town on trains and coaches.
They settled on beaches either side of the pier to picnic and listen to music.
The group had planned a trip to Brighton on Saturday but due to the Pride 2008 celebrations were diverted to Eastbourne.
Mandy Clark, from London, was visiting Eastbourne for the weekend and was horrified by the 'unimaginable amount of rubbish' her fellow Londoners left behind - which included broken bottles and cans, plates of half-eaten food and a tarpaulin covering.
She said, "It was a complete shock to see such a clean place violated so outrageously.
"They set up generators, unloaded food and drink by the van load, and were somehow allowed to set up sound stages and banks of speakers and there wasn't a policemen to be seen."
A spokesperson for Sussex Police said officers had not received any notification of the visit.
The spokesperson said an assessment was quickly made of the gathering and a joint meeting was held with representatives from the local council and community leaders from within the groups.
The spokesperson added, "As a result dedicated police officers were assigned to provide a high visibility presence and measures were put in place to deal with any associated disorder.
"Additionally members of Sussex Police Roads Policing Team were present to assist in the management of a large number of privately hired coaches that arrived throughout the evening taking the people home."
Tina Kliszcz, of Sandhurst Mews, Eastbourne, added, "After taking 40 minutes to travel by car along the seafront on Saturday, I was amazed at the seemingly unsupervised mess that I saw as I neared the pier.
"Eastbourne seemed to be invaded by people who neither cared less at the mountain of rubbish that was being discarded, or cared that pick ups and put downs by coaches and cars that were double parked were jamming the road between the pier and just after Treasure Island."
A borough council spokesperson said, "SITA and another of the council's contractors, Milhams, have done a fantastic job in clearing up the beach, working diligently to remove all of the 2.5 tonnes of litter before 8am on Sunday so that residents and visitors could enjoy the clean well cared for beaches they are used to.
"Although the level of noise and litter was regrettable the council acted quickly to return the seafront to normal."
Chief Inspector Dick Coates said, "Large numbers of visitors to the town is always good and shows what a safe and secure place Eastbourne is.
"I will though speak to the organisers if they wish to attend in future years to make sure they take all their rubbish home with them or use the bins provided.
"The mess left behind for the council to clear up was not acceptable. Visitors to our town are always welcome.
"I am very pleased to say that throughout the afternoon and early evening only one minor incident was reported to police."